How Sustainable are Biomedical Ontologies?

BioPortal is widely regarded to be the world's most comprehensive repository of biomedical ontologies. With a coverage of many biomedical subfields by 716 ontologies (June 27, 2018), BioPortal is an extremely diverse repository. BioPortal maintains easily accessible information about the ontologies submitted by ontology curators. This includes size (concepts/classes, relationships/properties), number of projects, update history, and access history. Ontologies vary by size (from a few concepts to hundreds of thousands), by frequency of update/visit and by number of projects. Interestingly, some ontologies are rarely updated even though they contain thousands of concepts. In an informal email inquiry, we attempted to understand the reasons why ontologies that were built with a major investment of effort are apparently not sustained. Our analysis indicates that lack of funding, unavailability of human resources, and folding of ontologies into other ontologies are the most common among several other factors for discontinued maintenance of these ontologies.